How weather affects fall colors

Weather factors, particularly temperature and moisture, can affect the display of fall colors across Michigan.

Fall Tisdale – Photo Credit: Julie Crick, MSU Extension.

Fall Tisdale – Photo Credit: Julie Crick, MSU Extension.

As summer activities begin to wind down, Michiganders begin to turn their attention to fall campfires, cool nights and some of the most spectacular fall color displays in the nation. The beauty of Michigan’s fall colors can obviously be attributed to the abundance of hardwood forested landscapes with a mixture of maples, oaks, and beech trees, which produce vivid orange, yellow and red colors. A factor in the fall color display that is not so obvious is the weather leading up to the shortening of the days, which is the cue for leaves to produce less chlorophyll and begin the fall show of color before losing their leaves for winter.

Why leaves change color

The leaves change color mainly in response to the decrease of daily sunlight. Photosynthesis, or the production of sugars that depend on sunlight, begins to slow down in response to the change in the amount of light. This leads to a reduction of chlorophyll, the pigment that supports photosynthesis and gives leaves their green color. When chlorophyll is reduced, other pigments in the leaves begin to show or are produced. The extent of red color and length of time leaf color is displayed is directly related to temperature and moisture conditions that occur before and during the period when the amount of chlorophyll in the leaves is diminishing.

Weather plays a role

The most brilliant leaf displays follow a period of warm days filled with sunshine and cool nights. During this weather cycle, leaves produce an abundance of sugars during the sunny days.The cooler nights and gradual narrowing of leaf veins in the fall, means that a majority of the sugars produced are trapped in the leaf. An abundance of sugar and light in the leaf lead to the production of vivid anthocyanin pigments, which produce red, purple and crimson colors. Yellow and gold leaf colors are produced by carotenoid pigments, which are ever-present in the leaves and are therefore less dependent on the aforementioned conditions.

Soil moisture also plays a role in the timing and brilliance of leaf color. The best displays are produced when the soil has been adequately moist throughout the year coupled with the aforementioned late summer weather. A late spring, or severe summer drought can delay the onset of color. A warm period during the fall can also decrease the intensity of fall colors by triggering early leaf drop before the colors have had a chance to develop.

Other factors also cause leaves to change color early or out of synch with their neighbors. Trees on the edge of low-lying areas, where cooler air collects at night, often display colors sooner than trees in an upland forested setting. Trees that are diseased or in decline may also display fall colors earlier than their healthy neighbors. Look for other signs, such as dead branches, wounds to the trunk or areas of root compaction to provide more information about a tree health issue.

What will the colors be in your neck of the woods? The variability of the conditions involved ensures that no two fall color displays will be identical year to year. However, scientists make predictions about the timing of fall colors, and yes, there is an app for that. Michigan State University Extension Professionals recommend that you check the timing, watch the weather and see if you can predict the intensity of your local fall color display.

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